Dihydroorotate dehydrogenase of Toxoplasma gondii - kinetic characterization and intracellular localization
Author: Hortua Triana, Miryam Andrea
Director(s)/Advisor(s): Zimmermann, Barbara Hanna
Publication date: 2010
Content type: doctoralThesis
Keywords:
Abstract:
The pyrimidine biosynthesis patway in the protozoan pathogen Toxoplosma gondii is essenial for parasite growth during infection. To investigate the properties of Dihydroorotate dehydrogenase (TgDHOD. TgDHOD exhibited a specific activity of 83.8 U/mg, a kcat of 89.2 sec-1 ± 1.5. a Km = 60.3 ±0.002 æM for L-dihydroorotate, and a Km = 28.9 æM ± 1.8 for decylubiquinone (QD). Quinones lacking or having short isoprenoid side chains yielded lower kcats and higher Kms than QD. As expected, fumarate was a poor electron acceptor for this family 2 DHOD. The determined for Redoxal and A77-1726 were 253.3 æM ± 13.3 and 91.2 æM ±2.2, respectively. The enzyme was not significantly affected by brequinar or TTFA, known inhibitors of human DHOD, or by atovaquone. TgDHOD exhibits a 157 ? residue N-terminal extension, consistent with potential organellar targeting, but bioinformatic analysis failed to reveal a consensus subcellular destination, Preliminary inmunolocalization studies of TgDHOD performed in intra- and extracellular parasites treated with the polyclonal antibodies raised against purified recombinant TgDHOD exhibited fluorescence that appeared to colocalize with the apicoplast in fluorescence was observed in -10% of mitochondria stained with Mitotracker Red in extracellular parasites. These findings suggest that TgDHOD is associated with both the apicoplast and mitochondrion, making it a member of a growing list of a metabolic enzymes that are dual targeted in T. gondii